1. Field of the Invention
The invention is related to diode lasers, and more particularly, to separating diode lasers from wafers.
2. Discussion of the Prior Art
Coherent light-emitting diodes having a GaAs-(Al,Ga)As double heterostructure, such as described in "Semiconductor Lasers and Heterojunction LED's" by H. Kressel and J. K. Butler, Academic Press, New York, 1977, are known to be efficient light sources for optical communications systems.
As is well-known, such diode lasers comprise layers of GaAs and (Al,Ga)As on an n-GaAs substrate. The final layer is a cap layer of p-GaAs. Metallized stripes, parallel to the intended direction of lasing, are deposited on the p-side of the wafer. Gold contact pads, somewhat smaller in area than the intended size of the diode laser, are deposited on the n-side of the wafer. The stripes and pads are for subsequent connection to an external electrical source.
The wafer is then cut in two mutually orthogonal directions to form the individual diodes. First, the wafer is cut perpendicular to the intended lasing facets into bars of diodes. Then the bars of diodes, following passivation of lasing facets, are cut into individual diodes.
Cutting of the wafer into bars is generally accomplished by cleaving the wafer through the substrate side, using an instrument such as a razor blade, knife, scalpel blade or the like. Control over length of the diode laser is consequently poor, and variation of diode laser length is great, with the result that longitudinal mode distribution and threshold current vary considerably from one diode laser to the next. Further, the gold contact pads must be kept thin in order to permit reasonably clean cleaving. Also, the thickness of the substrate is constrained in order to promote better cleaving. Finally, striations generated by the mechanical cleaving, if across the active lasing region, affect device yield, since such devices are consequently prone to degradation.